Some older digital cameras and iPhones suffer from a curse called shutter lag—a delay between the time you press the shutter button and the moment when the shutter actually fires.
Shutter lag occurs because the camera’s built-in computer must calculate exposure and focus. If you’re shooting fast-moving subjects, it’s easy to miss the shot you wanted.
The solution: give your camera a head start. Press and hold the shutter button partway, and the camera calculates focus and exposure. Now wait until the right moment arrives, then press the button the rest of the way.